Use sysconfig to determine stdlib paths for PyPy

[DanielNoord]

Steps

• Write a good description on what the PR does.

Description

3/3 of PRs mentioned in #1322

This was a little more difficult to fix. See the structure of their repository here.

Basically on PyPy sysconfig.get_path is having trouble getting to the correct folders. It returns '{installed_base}/lib-{implementation_lower}' (this can be seen by passing expand=False). However, on PyPy the stdlib is spread over two different folders.

It finds the first folder with sysconfig.get_path. I believe this is because sys.prefix/lib_pypy is symlinked to sys.prefix/lib-pypy. Note that I think we can use only sys.prefix (the standard for sysconfig.get_path) as the issue with sys.prefix overwriting in virtualenvs is the same as mentioned in #1323 and seems to be fixed from my testing. This allows to remove the try...except block.

For the lib-python/3 folder we can't seem to get sysconfig.get_path to work. I don't think the function is intended to be able to resolve a stdlib spread over two different directories. I think there was something strange going on in distutils that made get_python_lib(standard_lib=True, prefix=sys.base_prefix) return the lib-python one, as sys.base_prefix is still ~/.pyenv/versions/pypy3.7-7.3.7. Not sure why distutils resolves this into the lib-python directory with get_python_lib but it worked... To fix this we can simply tell sysconfig that it should look for another implementation_lower and then it will find the correct directory.
Note that I have not added the 2.7 version as I think we don't support it?

I'm not sure what the order of review will be, but in the last PR of these three we should also add a changelog and remove all remaining imports. That doesn't necessarily need to be this PR though.

Type of Changes

	Type
✓	🔨 Refactoring

Related Issue

[Pierre-Sassoulas]

We do not support python 2.7 anymore the last version supporting it is pylint 1.9.5 (I don't know for astroid).

[cdce8p]

Left some comments. Although we might get away without adding lib_pypy, the safe thing to do would be to match all paths to the current implementation (even if some aren't strictly necessary). As a side note: It shouldn't be necessary to remove lib-pypy.

This is STD_LIB_DIRS on Github actions (for pypy):

{'/home/runner/work/astroid/astroid/venv/lib-python/3',
'/opt/hostedtoolcache/PyPy/3.6.12/x64/lib-python/3',
'/home/runner/work/astroid/astroid/venv/lib_pypy',
'/opt/hostedtoolcache/PyPy/3.6.12/x64/lib_pypy',
'/home/runner/work/astroid/astroid/venv/lib/python3.6',
'/home/runner/work/astroid/astroid/venv/lib64/python3.6'}

--
Regarding the merge order. I think it would make sense to do this one next and close with #1323 where the changelog entry could be added.

[cdce8p]

Looks good, but we should also do that for platstdlib.

[DanielNoord]

Are there actually any differences? The example in the docs doesn't show a difference:
https://docs.python.org/3/library/sysconfig.html
In the removed code we also don't seem to get platstdlib?

[DanielNoord]

Added!

[cdce8p]

LGTM! Let's do it then!

[Pierre-Sassoulas]

Thank you @DanielNoord !